1. Field of the Invention
The present invention relates to a display apparatus and the method of manufacturing thereof. More particularly, the present invention relates to an organic light emitting diode (“OLED”) display apparatus, which is driven by thin film transistors (“TFTs”) formed on a substrate, and the method of manufacturing the TFTs on the substrate.
2. Description of the Related Art
Generally, a display apparatus is one type of interface apparatus that can help images be perceived by eyes through processing data from information sources.
There are many typical display apparatuses such as a liquid crystal display (“LCD”) device, a plasma display panel (“PDP”), and an organic light emitting diode (“OLED”) display apparatus. The OLED display apparatus has advantages, such as being an emissive device radiating light without a backlight, having a fast response time, and having a wide viewing angle as compared to an LCD. An OLED display apparatus includes an organic thin film sandwiched between electron injecting and hole injecting layers, and emits light by recombination of electron-hole pairs in the organic thin film that generates excitons emitting light according to their energy levels. OLED display apparatuses are divided into two kinds, a passive matrix type and an active matrix type.
In the active matrix type, an OLED display apparatus comprises a switching thin film transistor (“TFT”) connected to the data signal line which controls a data voltage, and a driving TFT which controls currents of an organic layer in accordance with the data voltage received from the switching TFT. In order to achieve the best characteristic of an OLED display apparatus, the two TFTs require different characteristics from each other. For example, while the switching TFT requires relatively high on-off current ratio (I on/I off), the driving TFT requires relatively high mobility and stability for enhancing high current driving ability. If off current of a switching TFT is increased, the voltage transmitted to the driving TFT is dropped and the OLED display apparatus may generate a cross talk problem. If an OLED display apparatus has low mobility and stability of the driving TFT, the current of the organic layer is reduced, and then it may generate an image sticking problem and shorten duration time of it.